Conventionally, a propagation delay time is measured in a communication network for the purpose of maintenance and management of the communication network or positioning with a mobile telephone (for example, see Japanese Patent Application Laid-Open No. 2005-130256).
FIG. 4 is a schematic diagram illustrating a conventional method for measuring the propagation delay time. In a communication network 200, a server 210 transmits a measuring packet a to a client 220. Then the client 220 that receives the measuring packet a sends back the measuring packet a to the server 210, the server 210 receives the sent-back measuring packet a, and the propagation delay time of the communication network 200 can be measured from the time taken for a repetition of the measuring packet a.